add fgs jupyter tutorial and fix some fgs impl issues

Author: refraction-ray

CHANGELOG.md

@@ -20,6 +20,10 @@
 
 - Fix `to_dlpack` for jax version >= 0.7.
 
+- Fix large eps issue in entanglement calculation of FGS.
+
+- Fix cmatrix non-refresh issue for `post_select` in FGS.
+
 ## v1.2.1
 
 ### Fixed

docs/source/tutorial.rst

@@ -19,6 +19,7 @@ Jupyter Tutorials
     tutorials/gradient_benchmark.ipynb
     tutorials/contractors.ipynb
     tutorials/stabilizer_circuit.ipynb
+    tutorials/fermion_gaussian_states.ipynb
     tutorials/operator_spreading.ipynb
     tutorials/optimization_and_expressibility.ipynb
     tutorials/vqex_mbl.ipynb